#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque<int> sec,pos;
int n,x,k;
long long sum;
int main()
{
    f>>n>>k;
    for(int i=1;i<=n;++i)
    {
        f>>x;
        while(!pos.empty() && i>=pos.front()+k)
        {
            pos.pop_front();
            sec.pop_front();
        }
        while(!sec.empty() && sec.back()>=x)
        {
            sec.pop_back();
            pos.pop_back();
        }
        sec.push_back(x);
        pos.push_back(i);
        if(i>=k) sum+=sec.front();
    }
    g<<sum;
    return 0;
}